GB1564378A

GB1564378A - Arc discharge lamp including a capacitor

Info

Publication number: GB1564378A
Application number: GB38752/77A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1976-09-21
Filing date: 1977-09-16
Publication date: 1980-04-10
Also published as: NL7610451A; ATA671077A; SE7710468L; US4134042A; FR2365208A1; DE2740468A1; AU2891177A; CH623427A5; JPS5339674A; AT355136B; FR2365208B3; BE858859A; SE442154B; AU505192B2; CA1102402A; JPS616995B2

Description

PATENT SPECIFICATION

( 11) 1564378 ( 21) Application No 38752177 ( 22) Filed 16 Sept 1977 ( 19) ( 31) Convention Application No 7 610 451 ( 32) Filed 21 Sept 1976 in ( 33) Netherlands (NL) ( 44) Complete Specification published 10 April 1980 ( 51) INT CL 3 HOIJ 61/56 H 05 B 41/23 HOIJ 61/54 ( 52) Index at acceptance HID 12 B 13 Y 12 81 12 82 12 B 47 Y 12 B 4 18 B 35 5 E 5 P 3 9 B 9 H 9 Y H 2 H 713 7 C LD 3 ( 54) ARC DISCHARGE LAMP INCLUDING A CAPACITOR ( 71) We, N V PHILIPS' GLOEILAMPENFABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it it to be performed, to be particularly described in and by the fol-

lowing statement:-

The invention relates to an arc discharge lamp intended for operation with alternating current, which lamp comprises two input terminals, a discharge tube provided with at least two main electrodes, an outer bulb, which envelopes the discharge tube, and a capacitor electrically connected to at least one of the main electrodes.

A prior art lamp of the type described above is, for example, disclosed in Patent Specification No 1,471,104 In this known lamp, the capacitor has a fixed value so that at the beginning of the starting procedurewhen the lamp tempeature is still substantially equal to the ambient temperature-the capacitor has the same properties as when the lamp is in operation This means that the capacitor can not have the optimum capacitance value for both the starting and operating conditions.

It is an object of the invention to provide a discharge lamp of the type described above wherein the capacitor has a suitable capacitance for each of the two conditions.

In a first group of arc discharge lamps according to the invention which are intended for operation with alternating current, such a lamp comprises two input terminals, a discharge tube provided with at least two main electrodes, an outer bulb which envelops the discharge tube, and a capacitor which is disposed wholly within the lamp and is electrically connected to at least one of the main electrodes, and is characterized in that the capacitor is a negative temperature coefficient (NTC) capacitor and that the input terminals are interconnected by a series arrangement of at least the capacitor and the whole of the discharge path between the said two main electrodes.

In a second group of arc discharge lamps according to the invention which are destined for operation with alternating current, such a lamp comprises two input terminals, a discharge tube provided with at least two main electrodes, an outer bulb which envelops the discharge tube, and a capacitor which is disposed wholly within the lamp and is electrically connected to at least one of the main electrodes, and is chaacterized in that the capacitor is a negative temperature coefficient (NTC) capacitor and is included in a branch connected solely across the two main electrodes so that, for both current directions, it is in parallel with the whole of the discharge path between the said two main electrodes.

An advantage of the two groups of arc discharge lamps according to the invention is that the NTC capacitor can have, both at the beginning of the procedure and also during the operating condition of the lamp, a capacitance value which is adapted thereto.

The following should be noted by way of explanation With a discharge lamp of the first group the NTC capacitor forms a stabilisation ballast of the discharge tube In the cold state of the discharge tube, i e at the beginning of the starting procedure, the NTC capacitor has a relatively large capacitance and, hence a relatively low impedance For lamps which have no stabilisation ballast other than this NTC capacitor, as well as for discharge lamps in accordance with the first group of the invention which have an additional inductive ballast in series, the initially low impedence value of the NTC capacitor results in a fairly high starting current of the lamp and, therefore, that the lamp rapidly reaches the operating condition Once the lamp is in the operating condition then the NTC capacitor, which is included in the lamp, will assume a higher temperature This results in a substantial decrease of its capacitance so that its impedence increases As a result the lamp current is then lower than the starting current.

If_ 1,564,378 Should the capacitor have been a stabilisation ballast of fixed capacitance value this would not have given the advantage of the accelerated starting of the lamp With a discharge lamp-according to the invention-of the second group the NTC capacitor and the discharge path between the main electrodes of the discharge tube are in parallel branches Here the NTC capacitor is intended, for example, to promote starting of the lamp This capacitor may, for example, also serve to improve the power factor (cos q) of the electric circuit in which the discharge lamp will be included.

With a discharge lamp-according to the invention-of the second group, this parallelcapacitor is again an NTC capacitor An advantage thereof is that the capacitance value-is relatively high during the beginning of the starting procedure and relatively low if the lamp is in the operating condition This may mean an easy start and no disadvantages of this parallel capacitor during the operating condition of the lamp.

The capacitance value of the NTC capacitor may change, for example, by a factor of with a change in temperature of 1750 C.

A lamp according to the invention may, for example, be a high-pressure discharge lamp or a low-pressure discharge lamp.

Some embodiments according to the invention will now be further explained with -reference to the accompanying drawings, in which:

Fig 1 shows a partly longitudinal section, partly elevational view, of a discharge lamp according to the invention; Fig 2 shows the electric circuit in the lamp of Fig 1 as well as a stabilisation coil and further connecting wires of a power supply circuit in which this lamp has been included; Fig 3 shows a partly longitudinal section, partly elevational view, of a second discharge lamp according to the invention; and Fig 4 shows the electric circuit in the second lamp according to the invention as -well as a stabilisation coil and other connections of a power supply circuit in which this second lamp has been included.

Fig 1 shows a high-pressure mercury vapour discharge lamp provided with a quartz glass discharge vessel 1 which contains iodides and a mixture of rare gases, such as neon and argon, which considerably decrease the ignition voltage of the lamp.

Tungsten electrodes 2 and 3 are disposed at the respective ends of the tube 1 The electrodes 2 and 3 are supported by currrent leads 4 and 5 respectively which are passed by means of molybdenum foils 6 and 7 respectively through the pinched feet 8 and 9 respectively in a vacuum tight manner Tube 1 is suspended in a glass outer bulb 10 by means of metal strips 11 and 12 which clamp around the pinched feet 8 and 9 respectively and are connected to current conductors 13 and 14 respectively which serve as current supply elements for the electrodes 2 and 3 respectively The current conductors 13 and 14 are led out in a vacuum-tight manner 70 through the outer bulb 10 Current supply conductor 14 is connedted to one side of an NTC capacitor 15 housed in a base 16 of the lamp This capacitor has a dielectric of, for example, a barium titanate The other side of 75 NTC capacitor 15 is connected to a connecting contact (input terminal) 17 of the lamp base Current conductor 13 is connected direct to another connecting contact (other input terminal) 18 of the lamp base 16 80 Fig 2 shows, in circuit schematic form, items 1, 2, 3, 8, 15 and 17 of Figure 1 Additionally, the terminal 17 is connected to a power supply terminal 20 through an inductive stabilisation ballast 19 and terminal 85 18 is connected to a power supply terminal 21 The voltage which is applied between the terminals 20 and 21 is, for example, approximately 220 volts, 2500 Hertz.

In the situation that the specified voltage is 90 applied between the terminals 20 and 21, the NTC capacitor 15, on starting of the tube 1, will first show a high capacitance, that is to say a low impedance The electric current through the tube 1 is then also relatively high 95 As a result the tube will rapidly arrive in its operating condition Once this has happened, owing to the generation of heat in this tube, the NTC capacitor 15 in the lamp base 16 will be heated so that its capacitance value 100 decreases and its impedance increases Consequently a reduced current then flows through the discharge tube 1.

In a practical embodiment the power of the lamp is approximately 400 Watts, the self 105 inductance of the stabilisation component 19 is approximately 3 m Henry and the capacitance value of the NTC capacitor 15 is approximately one micro Farad at room temperature-( 25 C) and approximately 0-6 micro 110 farads in the operating condition of the lamp (approximately 150 degrees Centigrade) The starting current through the tube 1 is then approximately 8 Amps and the current in the operating condition is approximately 3 115 Amps.

Fig 3 shows a high-pressure sodium vapour discharge lamp having a discharge tube 31 which is enveloped by an outer bulb 32 The discharge tube comprises, in addition 120 to sodium and mercury, a gas mixture of neon and argon to facilitate starting Reference 33 indicates a base of that lamp The power of the lamp is approximately 400 Watts 125 The end of the tube 31 which faces away from the base 33 is connected to a supply strip 34 In its turn this strip is connected to an electric supply conductor 35 having an extension 36 which serves for supporting and 130 1,564,378 centring the discharge tube 31 in the outer bulb 32 Furthermore the supply conductor is connected at point A to the threaded portion of the base 33.

The end of the discharge tube 31 which faces the base 33 is connected to an electric supply conductor 37 which leads to a centre contact B of the base 33 An electric connection 39 feeds current from conductor 37 to the relevant tube electrode A section 40, in the extension of the conductor 37 has a supporting function only, namely to provide a flexible support for the tube 31.

An NTC capacitor 41 is housed in the space between outer bulb 32 and discharge tube 31 and is connected between the conductors 35 and 37 so that it shunts the discharge path of the discharge tube.

The discharge tube 31 (see Figs 3 and 4) is provided with a first main electrode 43 and a second main electrode 44 The electrode 43 is connected to the lamp input terminal A which is connected to a power supply terminal 46 through a stabilisation impedance 45 The internal electrode 44 is connected to the lamp input terminal B This terminal B is connected to a power supply terminal 47 Reference 41 again indicates the shunt NTC capacitor.

The circuit of Fig 4 operates as follows.

First a voltage is applied between the terminals 46 and 47, for example of 220 Volts, Hertz In the first instance the NTC capacitor 41 is at ambient temperature and consequently has a high capacitance The discharge tube 31 starts and this is promoted by the presence of the NTC capacitor 41 in the high capacitance (low impedance) state.

Owing to the subsequent generation of heat in the discharge tube, NTC capacitor 41 will be heated and, as a consequence, the capacitance value of this capacitor decreases to such a value that it virtually has no further effect in the circuit.

In a practical embodiment in the case of Fig 4 the stabilisation element 35 has a selfinductance of approximately 015 Henry, the NTC capacitor 41 has at room temperature ( 250 C) a capacitance of approximately one micro Farad and in the operating condition of the lamp, that is to say at a temperature of approximately 200 'C, a capacitance of approximately 0 1 micro Farad This low capacitance value hardly affects the behaviour of the lamp in the operating condition.

In this example (Figs 3 and 4) the change in capacitance of the NTC capacitor is greater than in the example which was described with reference to Figures 1 and 2 This is due to the fact that the capacitor 41 is very considerably closer to the discharge tube 31 than capacitor is to discharge tube 1 and is consequently heated to a higher temperature.

In the two described embodiments the NTC capacitor has a lower capacitance in the operating condition of the lap than in the starting condition of the lamp Therefore each of these values is better suited to the particular condition pertaining than is the value of a single fixed-value capacitor.

A lamp according to the invention may alternatively be, for example, a low-pressure sodium arc discharge lamp, the circuit for supplying a lamp according to the invention may also comprise a separate starter.

The NTC capacitor may be used in combination with a capacitor having a fixed capacitance value.

Claims

WHAT WE CLAIM IS:-

1 An arc discharge lamp intended for 80 operation with alternating current, which lamp comprises two input terminals, a discharge tube provided with at least two main electrodes, an outer bulb which envelops the discharge tube, and a capacitor which is 85 disposed wholly within the lamp and is electrically connected to at least one of the main electrodes, characterized in that the capacitor is a negative temperature coefficient (NTC) capacitor and that the input 90 terminals are interconnected by a series arrangement of at least the NTC capacitor and the whole of the discharge path between the said two main electrodes.

2 An arc discharge lamp intended for 95 operation with alternating current, which lamp comprises two input terminals, a discharge tube provided with at least two main electrodes, an outer bulb which envelops the discharge tube, and a capacitor which is 100 disposed wholly within the lamp and is electrically connected to at least one of the main electrodes, chaacterized in that the capacitor is a negative temperature coefficient (NTC) capacitor and is included in a 105 branch connected solely across the two main electrodes so that, for both current directions, it is in parallel with the whole discharge path between the said two main electrodes.

3 An arc discharge lamp substantially 110 as hereinbefore described with reference to Figures 1 and 2, or to Figures 3 and 4, of the accompanying drawings.

R J BOXALL, Chartered Patent Agent, Century House, Shaftesbury Avenue, London WC 2 H 8 AS.

Agent for the Applicants.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon), Ltd -1980.

Published at The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY from which copies may be obtained.